AC and % Damage reduction (in General)

What is the relationship between AC and damage reduction?

Specifically, I'm wondering how much I have to enchant a kite shield to get a 3% damage reduction to balance the 3% magic penalty.

Short answer, 0.21% per AC. Long answer, Help -> Armor.

Is a 3% magic penalty worth exactly 3% damage reduction, though?

nope, You have to factor in that only +'s protect against magic damage.

You're missing the point. I was asking if/how Grant has figured out that 3% damage reduction is worth sacrificing 3% of his FB/AS/AMF or whatever. Anyway, the magical damage thing is in Help.

How much damage reduction your shield gives also depends on the total AC you already have. Each AC point blocks (roughly, but we're averaging here, so it's OK) 0.21% of the total damage. But what you're asking is how much AC on the kite is needed to block 3% of the remaining damage.

If you already have 100AC for example, then you are already blocking 21% of the total damage. The remaining damage is then 79% of what you would receive when your minion was naked. 3% of that 79% is 2.37%, or roughly 11AC.

If you already have 200AC, then ithe kite only needs to add 8AC to be worth the 3% magic penalty. So a base kite is already worth it for you, if your other armor has 200AC (I doubt that would be mage armor ;)

With no other armor, you need a +6 kite.

I understood salt, but bartjan's last paragraph made my head hurt :)